5.3.1 Planning

Preoperative planning of the surgical implantation is important, due to the various differences in the facial anatomy and especially in the PPF. This affects not only between different patients, but also within one patient, as the left side may be different from the right [18], [10].

In all patients, the presence of dental pathology should be excluded prior to implantation as this may result in postsurgical infection of the implant site. To address these issues, prior to surgery, a panoramic view, dental cone beam computed tomography (CBCT), or computed tomography scans (CT) of the oral cavity an the maxillary sinus should be performed [19]. Interpretation and description of the radiological investigations should focus on signs of osteopathology including infection, pericoronitis, and impacted wisdom teeth as well as the morphology of the pterygomaxillary fissure. The latter bears importance as the lead diameter of the microstimulator is 1 mm. A minimum width of the fissure of 1.2 mm is preferable.

A unique challenge in CH is constituted by patients who have been treated for many years with pulse therapy of corticosteroids as this may lead to osteoporosis, increasing the risk of perioperative posterior maxillary wall fracture [10]. These, as well as the described radiological findings, weigh in on the final confirmation of patient eligibility at the surgeon’s discretion. Thus far, in the published studies, no patients have been rejected on the basis of surgical ineligibility but some have had preoperative dental procedures. On the establishment of surgical eligibility, the manufacturer performs 3D modeling and makes a recommendation for stimulator size—short (3.6 cm), medium (4.4 cm), long (5.2 cm), and extra-long (6.0 cm). As power and control is provided by the RC, these recommendations also figure the resulting depth of the microstimulator housing as this is essential for a functioning connection.

5.3.2 Surgery

All insertion procedures have to be done under general anesthesia. The risk of dislocation of the stimulator during local anesthesia is quit to high, as well as pain attacks during implantation caused by manipulation of nerval structures inside the PPF during the insertion procedure. As the procedure is sterile contaminate, it should be performed under antibiotic cover and with prior oral decontamination per local guidelines. Local anesthetic with adrenaline may be applied to reduce bleeding and postoperative swelling and pain. The microstimulator is inserted transorally. Depending on the patients’ dentition, gingival buccal approach, a crestal incision, or a marginal incision can be performed. After subperiosteal tissue dissection from the lateral and posterior maxilla, the microstimulator can be placed with its stimulating electrodes into the PPF of the affected side. The microstimulator is then fixated with its osteosynthesis plate to the anterior wall of the maxillary sinus by using three osteosynthesis screws [19] (Fig. 5.3).

The procedure is aided by the ATI surgical introducers, starting with the SI-100 (Fig. 5.4a), which is a curved subperiosteal elevator; the posterior lateral maxilla is prepared by subperiosteal dissection into the PMF. When reaching the expected area inside the PPF, a.p. and lateral fluoroscopy is used to verify the position of the SI-100 (Fig. 5.5). The SPG is expected in the lower third of the distance in between the two anatomical structures “foramen rotundum” and “Vidian canal” [10]. If position is good, the SI-110 (Fig. 5.4b) is used and also inserted into the same position inside the PPF (Fig. 5.6). Both instruments, SI-100 and SI-110 allow for blunt atraumatic subperiosteal dissection while maintaining close contact to the posterior wall of the sinus to avoid trauma to the surrounding tissues [10]. The surgeon can optimize the contour of the instruments by adapting the curvature of the instruments to the shape of the posterior maxillary sinus curvature and may avoid soft tissue destruction and inside the infratemporal fossa and minimize intraoperative bleeding. When the SI-110 is placed at the entrance of the PPF, the lead blank (LB-100) (Fig. 5.6) is used to create an implant path within the PPF [10].

In some anatomical variations, the SI-120 may not fit into the PPF due to a small entrance and may be precluded. In those cases, placement of the microstimulator may be achieved by inserting the microstimulator along the insertion groove and split tip of the SI-110 (Fig. 5.7). Especially in those cases, periodic images are necessary to verify correct positioning of the microstimulator inside the PPF at the expected target point.

If anatomy allows, SI-120 can be used to insert the microstimulator into the PPF. The microstimulator is then placed into the SI-120, which is inserted using the existing surgical plane created by the SI-100 or SI-110. Here too, repeated fluoroscopy is recommended to visualize the position of the SI-120 and to maintain the trajectory toward the cranial and medial aspect of the PPF [10] (Fig. 5.8).

If target placement is achieved and the positioning of the microstimulator is checked against the DRR images, it can be pushed slightly forward and be removed from the SI-120 anchoring hub. While pushing the body against the lateral wall of the sinus, the SI-120 is retracted as the sheath opens around the lead. Finally, three 4–6 mm osteosynthesis screws are used to fixate the microstimulator on the anterior wall of the maxillary sinus and final anterior–posterior and lateral fluoroscopy is performed to check the final position (Figs. 5.9 and 5.10).

Microstimulator function is checked prior to insertion and closing suturing. After surgery, correct placement of the device is assured by intraoperative 3D-CT if possible, or a postoperative 3D-CT. If necessary, placement may be revised. The procedure is considered minimally invasive—comparable in extent to that associated with wisdom tooth extractions or dental implants procedures. The average duration of the surgery for the first 99 patients was 80 min (range 25–175) [19].

5.3.3 Surgical Intraoperative Navigation

When possible, intraoperative navigation can also be used for this procedure. Navigation technique allows, especially in the initial phase of this procedure, precise placement of the surgical introducers without using radiation [20]. In preparation for navigation CBCT or CT scans of each patient are required. Those images allow, next to a detailed analyzation of the PPF, whether the microstimulator implantation procedure was suitable and to estimate the necessary length of the SPG microstimulator. Overwork of all scans and files are performed for each patient separately and are reconstructed as DRR for intraoperative comparison (Figs. 5.11 and 5.12). All preoperative planning is performed using special software solutions. Those are available by different companies. All 3D-CBCT data and the virtual treatment plan are then uploaded into the used navigation system (Fig. 5.13).

Surgical implantation using navigation is also performed under general anaesthesia. Before starting implantation, marker spheres of the used system have to be attached to the patients’ calvarian bone, called skull reference array (SRA) (Fig. 5.14). Further marker spheres are attached to the surgical instruments (SI-100 and SI-110) (Fig. 5.15), which are used as described before. This procedure enables the surgeon to visualize the exact position of the instruments inside the patients’ anatomy during surgical insertion without the use of radiation. The system displays the actual position during insertion of the instruments inside the PPF (Fig. 5.16). When the expected position inside the PPF is reached, insertion of the microstimulator can be done using the SI-120 [20].

Insertion is performed using the SI-100 or SI-110 as a guided tool. After implantation of the SPG microstimulator, real-time verification of correct placement can be done by conventional anterior–posterior and lateral fluoroscopy. After fixation of the SPG microstimulator on the zygomatic process with two to three osteosynthesis screws, final confirmation of the exact position can be done using intraoperative 3D-CBCT/CT scans. The electrode tip has to be positioned in close vicinity to the previously defined target points (Vidian canal and foramen rotundum) [10, 20]. The final scans can be matched with the preoperative 3D-CBCT or CT scans using built-in image alignment software integrated to most navigation systems. Image fusion allows direct comparison of the expected SPG microstimulator position and the real-time result (Fig. 5.17) [20]. Due to direct verification of the position or misplacement, immediate revision and reinsertion are possible [20].

5.3.4 Postsurgical Aspects

It is relatively common that the patient wake up with a CH attack immediately after the general anesthesia, which the patient of course should be informed in advance. Postoperatively, patients should pay special attention to avoiding pressure on the cheek on the affected side. Diet should be limited to soft and cool food on the first postoperative day. Smoking should be avoided in the first couple of days. Oral decontamination, for example, Chlorhexidine 0.12% should be continued twice daily for 1 week. Peroral antibiotics on the first three postoperative days are recommended. One to two weeks after surgery, the wound should be inspected and sutures removed if resorbable suture is not used. Infections may be treated at this point using debridement or intravenous antibiotics. The patient can subsequently receive normal dental treatment, filling and crown therapy, etc., but the dentist should avoid injection of local anesthetic behind the tuber maxillae on the operated side to prevent damage to the electrode or inappropriate relocation of the lead.

5.3.5 Programming

First programming and stimulation can be attempted 2 weeks following insertion. Earlier attempts are generally avoided as healing is still ongoing. The adjustable parameters for the Pulsante™ system include pulse frequency, width, and amplitude. Furthermore, the anode/cathode state of the six electrodes on the lead can be changed. The overall guiding principle of programming is to obtain a sensation of parasthesia in the posterior nasopharynx. The reasoning behind this is that this is the innervation area for the sensory components of the SPG. Thus, if parasthesia is obtained here, by inference, the SPG must be in the stimulation field. The programming is done by a technician in cooperation with the patient. Several attempts, weeks apart, may be necessary before a suitable setting is found.

5.3.6 Side Effects

The microstimulator is small and, barring surgical side effects, does not give rise to cosmetic issues. However, a majority of patients experience postoperative sequalae. These include pain and swelling (47%) and sensory disruptions (67%) [14, 19, 21]. Resolution of these surgical side effects is usually swift, within 2–3 months, and would typically be classified as mild–moderate. Some patients experience a transient increase in attacks in the days and weeks following surgery. No late side effects (24 months) have been reported. Most importantly there has been no need for repeated surgery due to lead breaks or migrations [21]. Special consideration has been given to the possibility of contralateral attacks or even side shifts. However, it does not appear that that SPGS can be causally related to observed contralateral attacks, which do occur with some regularity in CH in general [22].

5.4 Clinical Evidence